Process of making nitrocellulose films and similar products



Feb. 16, 1932. J. B. WELLS 1,845,377

PROCESS OF MAKING NITROCELLULOSE FILIS AND SIMILAR PRODUCTS Original Filed Feb. 10, 1928 amen doc,

Jackson 3. WeZLs,

attain;

Patented F eb, 16, 1932.

UNITED STATES PATENT OFFICE JACKSON 3. WELLS, OFROCHESTER, NEW YORK, ASSIGNOB TO EASTMAN KODAK (30H- PANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW.YORK

PROCESS OF MAKING- NITROCELLULOSE FILMS AND BM IROID'UGI'S Application filed February 10, 1928, Serial No. 258,861. Renewed larch 9, 1881.

. This invention relates to processes of making nitrocellulose films and similar products,especially processes in which the films are set by liquid baths instead of by evaporation. One object of the invention is to provide an inexpensive process of this nature which will produce flexible, transparent, nitrocellulose films, filaments, etc., rapidly-with minimum fire-risk and with maximum recovery of the solvents employed. .Another object is to provide a process of this nature which can be carried out in a relatively small and simple apparatus. A still further object is to provide a process, in which cloudiness in the films is avoided in spite of the use of rapid or aqueous setting baths. Other ob-- jects will hereinafter appear.

In the accompanying drawing the single figure is a diagrammatic side elevation, with the top broken away, of one form of apparatus in which my process may be carried out, the relative sizes of the parts being ex-- aggerated for the sake of clearness.

I have found that the desired objects can be attained by shaping into film or filament form a nitrocellulose solution or dope containing methyl alcohol and afmonohydroxy aliphatic alcohol of low volatility which is at least partially soluble in water, and setting it, while in this form, by treatment withan aqueous bath. While plain cold water may be used, I prefer to employ a setting bath in which there is a nitrocellulose solvent, miscible with water but of insufiicient amount to prevent the setting action, said solvent regulating the setting operation. For example, a bath of water and methyl alcohol has proven to be very useful.

The presence of an alcohol of low volatil ity in the dope, such'as normal butyl alcohol for instance, has been found to be of special benefit, during the setting step, because it lessens the danger of forming whitish or clouded defects in thefilm. In fact, typical rapid filmssetting conditions, which have produced clouded products from plain nitrocellulose-methyl alcohol dopes, have been found to produce clear transparent films vwhen applied'to similar dopes containing a higher alcohol. This tendency of the higher preceding and'subsequent steps. For example, considerable dehydration of washed nitrocellulose fibers must be accomplished before a film dope can be made from them. The use of normal butyl alcohol for this purpose is disclosed in U. S. Patent No. 1,398,911, .Seel, November 29, 1921. It forms a mass of nitrocellulose fibers containing about 40 to 60% of butyl alcohol. This, when dissolved in methyl alcohol, as described in U. S. Patent No. 1,380,258, Seel, Combsand Kemp, May 31, 1921, produces a dopehaving the desirable properties formaking film by my present process. After the filmsare formed, they are coated to form photographic films; and the continued presence of a higher alcohol, such as butyl alcohol, in such films promotes better wearing qualities and increasedflexibility, as described in said last-named patent. It will, therefore, be seen that the higher alcohol passes successfully from the dehydration through my film-forming operation to the finished films, and is a beneficial ingredientnot a passive diluent-during such operation.

I shall now describe one Way of carrying out my process, by way of illustration, but it will be understood that the invention is not limited to the details thus given, except. as indicated in the appended claims. 100 parts by weight of cellulose nitrate fibers, of the type usually made up into film, are dehydrated with butyl alcohol and pressed until they contain from 30 to 100, say 50, parts by weight of butyl alcohol in the mass, as indicated in the hereinabove cited patents.

This mass is then dissolved in 300 to 1000 forming operation thatit fits in @both with v The lower part of this trough is provided with accurate edge pieces 2, 3, the latter be-' 8. This surface may be that shown in U. S.

Patent No. 1,466,733, Sulzer, September 4., 1923, but any other suitable surface, such as polished electro-deposited chromium, may also be used. The wheel 8 turns in the direction of the arrow, the sheet of dope on the surface 7 passing through a chamber 9. In this chamber the film-shaped body 5 of dope is still in a slowly fiowable condition and can, therefore, settle under the influence of gravity sufiiciently to enable the thickness of the layer to equalize. In other words, if portions of the layer are slightly too thick and other portions are slightly too thin, in spite of the accuracy of edge pieces 2 and 3, these inequalities will gradually work out in chamber 9 by the settling of the higher portions and the raising of the lower portions.

The equalized film-form layer 5 is then carried by continued revolution of the wheel 8 into the setting bath 10. The latter can be conveniently contained in a vessel which is substantially concentric with and spaced from the outer surface 7 of the wheel 8, as indicated in dotted lines in the drawing.

' While other forms may be used, this has the advantage of enabling the liquids of the bath to enter by pipe 11 and pass in a direction counter to the movement of the film, finally leaving the apparatus through exit pipe 12. As the setting bath proceeds from pipe 11 to pipe 12 in the direction of the arrows, it becomes more and more charged with methyl alcohol, which it extracts from the layer 5 on the surface 7. Conversely the layer 5 starts to set when it enters the bath adjacent the pipe 12 and gradually gives up more and more of its methyl alchohol to the bath as it proceeds toward the entrance pipe 11. In other words, the more firmly the film becomes. set and the more it loses the methyl alchohol, the stronger is the setting bath with which it contacts. I Since the bath, when it. leaves pipe 12, contains its maximum per.- centage of methyl alcohol, it is in the best condition for the recovery of the latter by {he usual processes, say by fractional distilation.

While I can introduce plain water through] pipe 11 as the initial ingredient of the setting ath, and allow the latter to increase in .methyl alcohol content, as it extracts methyl alcohol, during its passage through the apparatus, I- prefer to. introduce through the pipe 11 a mixture of a non-solvent for'the nitrocellulose,'such as water, and a solvent for it, such asmethylalcohol. A 50% aqueous solution by weight of methyl alcohol-has proven to be very useful. This becomes stronger as it proceeds through the apparatus to the exit pipe 12, by reason of the extraction of methyl alcohol from layer 5, and entrance of water into the film.

Of course, in any event there is some extraction of the higher alcohol, such as butyl alcohol, from the film, but there is always a substantial amount of it left in the film to maintain flexibility and wearing qualities in the latter. In fact, the rotation of the wheel 8, the rate of flow of the bath 10, the strength of the bath 10, and the length of the bathing chamber are always coordinated so as to leave the film with a useful content of the higher alcohol, say of the order of 1 to 10% of the weight of nitrocellulose; but this may be considerably higher, say 20%, depending upon the extent of curing or drying after the set film is stripped from the surface 7. It'will thus be seen that there is considerable latitude in the content of butyl alcohol in a film stripped from the surface 7 and the point' where the layer 5 of dope is deposited upon 7, there may be located any suitable cleaning or polishing apparatus, such, for instance, as

that described in U. S. PatentNo. 1,187,929,

Reid, June 20th, 1916. A pipe 15 is provided with fine perforations in its under side through which water is sprayed onto the surface 7. This pipe is parallel to the axis of drum 8. The cleaning liquid is not allowed to How down the surface 7 to the stripped film 51 or the bath 10, but is taken up by a dam in the shape of a hollow roll 16 having its periphery covered with a layer of soft rubber 17 through which a series of fine apertures are provided communicating with the interior of the roll, the latter being connectedto a vacuum apparatus, thus suckin the water through the dam and out of t e apparatus. The surface of the drum may be given a final conditioning by an absorbent roll 19, held against the surface by an adjustable spring20. Since the innerside of the film,'whieh is' stripped from the surface 7, is kept from contact' with liquids, and since the outer surface passes over smooth roll 13, and is squee'geed. -the-film 51 carries little or no surface liquid, and is-in' condition to be dried, cured and coiled by the known methods here 1 by the'jlatter tofore used in the production of nitrocellulose films by evaporation.

The trough 1 maybe kept above room temperature if desired, to keep the dope 6 at the ri "ht viscosity for formation of the layer 5, an may be covered to prevent the loss of volatile solvents. Both of these expedients, being well known in the art are, for the sake of simplicity, omitted from the drawing. The bath 10 may vary in temperature over a considerable range, although, in general, it is preferable to operate at lower temperatures, the higher the percentage of water in the bath 10. For example, it pure water be introduced through pipe 11, a temperature of about 4 C. is useful. But with baths containing 50% or more of methyl alcohol, there is no need for such low temperature. I usually prefer, however, to keep the entire apparatus, with the exception of trough 1, at or below room temperature, say 23 (3., because with higher temperatures the tendency towards cloudiness becomes greater.

My process may be applied to films of thicknesses customarily employed in the photographic art, but thicker ones, and even somewhat thinner ones, may be obtained in a state of satisfactory transparency, flexibility and strength. The setting action imparts sufficient strength to the film to allow it to be stripped from the surface 7 in fact, the setting action seems to counteract any harmful sticking tendency of the dope on the surface 7.

While I prefer to use normal butyl alcohol, because it is most readily available commercially, my process may be carried out with other monohydroxy aliphatic alcohols having a low volatility, such as isobutyl alcohol, and the different isomeric amyl alcohols, or mixtures of them, commonly available in fusel oil. It will be noted that these all have boiling points somewhat above that of water.

In the preferred form of my process the methyl alcohol used in the dope contains less than 1% of water and the dehydrated nitrocellulose fibers containing the butyl alcohol contain less than about 2 or 3% of water.

Consequently, the water content of the mixed (lope is of the order of 1%. There is no objection to carrying the dehydration below this point, but the solvent power of methyl alcohol for nitrocellulose rapidly falls ofi as the water content increases, so it is undesirable to'exceed the percentages given.

While I have indicated a cylindrical wheel surface as a suitable one to carry the filmshaped dope when it passes through the setting bath, it will be understood that any of the well known forms of surfaces maybe substituted, such as a belt havinga polished even face.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is: c

l. The process of making transparent,

' bath.

2. The. process of making transparent, flexible, nitrocellulose products of a form having great length relative to width and thickness, which comprises the steps of imparting such form to a solution of nitrocellulose containing an excess of methyl alcohol and a monohydroxy aliphatic alcohol of low volatility which is at least partially soluble in water, removing said excess while it is in said'form by treatment with a setting bath, which is a solvent of methyl alcohol and a non-solvent of nitrocellulose, removing the set product from said bath and drying the same.

3. The process of making transparent, flexible, nitrocellulose products of a form having great length relative to width and thickness,

which comprises the steps of imparting such .form to a solution of nitrocellulose in methyl alcohol containing normal butyl alcohol, and treating it while in said form with an aqueous setting bath containing methyl alcohol.

4. A process of making transparent, fleX- at'ility which is at least partially soluble in water, to 100 parts of nitrocellulose and treating it while'in said form with an aque- -ous setting bath containing methyl alcohol,

and stopping said treatment while a residuum of said alcohol of low volatility remains in said film.

5. The process of making transparent, flexible, nitrocellulose film, which comprises the steps of imparting a film-form to a solution containing 100 parts of nitrocellulose, 30 to 100 parts by weight of normal-butyl alcohol, and 300 to 1000 parts by weight of methyl alcohol, and treating it while in said form with an aqueous setting bath'containing at least 50% of methyl alcohol. y y

6. The process'of making transparent, flexible, nitrocellulose products of a form having great length relative to width and thickness, which comprises the steps of imparting such form to a solution of nitrocellulose in methyl alcbhol containing normal butyl alcohol and treating it while 'm'said form with an aqueous setting bath containing methyl alcohol and normal butyl alcohol.

7. The process of making transparent, flexible, nitrocellulose film, which comprises the steps of forming on a polished surface a layer of nitrocellulose dope containing methyl alcohol and a monohydroxy aliphatic alcohol of low volatility which is at least partially soluble in water, equalizing the thickness of said layer on said surface, treating said equalized layer while on said surface, with a set ting bath containing a liquid which is miscible with methyl alcohol but a non-solvent of nitrocellulose, and an amount of methyl alcohol inshflicient to prevent setting of said layer, and removing from said surface the film thus prepared.

8. The process of making transparent, flex- ;ible, nitrocellulose film, which comprises the steps of forming on a polished metallic surface a clear Viscous layer of nitrocellulose dissolved in a mixture of methyl and normal butly alcohols, allowing said layer to settle to lessen inequalities of thickness, treating the equalized layer, while on said surface,

with an. aqueous setting bath containing an amount of methyl alcohol to prolong the settingaction without stopping it, and removing from said surface the film thus prepared.

9. The process of making transparent, flexible, nitrocellulose films, which comprises the steps of forming into film-shape a nitrocellulose dope in which the nitrocellulose is dissolved in a mixture of methyl alcohol and a monohydroxy aliphatic alcohol of low volatility which is at least partially soluble in water, and treating it while in said shape to an aqueous setting bath containing a nitrocellulose solvent, the proportion of the latter being decreased as the setting proceeds.

10; The process of making transparent, flexible, nitrocellulose films which comprises the steps of forming on a polished surface a clear viscous layer of nitrocellulose dissolved in a mixture of methyl and normal butyl alcohols, moving said layer and an aqueous setting bath containing methyl alcohol relative to each other while the layer remains on said surface and in contact with said bath,

the latter being lowest in water content at the start of said relative movement and highest at the end thereof.

Signed at Rochester, New York this 8th day of February, 1928.

. JACKSON B. WELLS. 

